1. Field of the Invention
The present invention relates to a measuring apparatus, a measuring method, and a processing apparatus.
2. Description of the Related Art
Conventionally, an incremental encoder and an absolute encoder each having a different output format are present as measuring apparatuses for measuring positions and angles. Examples of a linear encoder for position measurement include an incremental linear encoder for measuring a relative position (change in position or displacement) and an absolute linear encoder for measuring an absolute position. Furthermore, examples of a rotary encoder for angle measurement include an incremental rotary encoder for measuring a relative angle (change in angle or displacement) and an absolute rotary encoder for measuring an absolute angle. In addition, an optical encoder and a magnetic encoder each having a different operation principle are present. Of these, in an optical encoder, a scale is irradiated with light emitted from a light source, and light transmitted through the scale or light reflected therefrom is received by a photoelectric conversion element. The light source and the photoelectric conversion element are mounted on an object to be moved or rotated and the scale is mounted on a fixing side serving as a reference or vice versa. In an incremental encoder, evenly spaced transmission films or reflection films are machined on a scale and received light intensity is a sine wave having a constant cycle. A signal processing device counts the wave number of the detected sine wave signals. The phase in a cycle is finely divided so as to improve measurement resolution and accuracy. On the other hand, in an absolute encoder, a transmission film or a reflection film having the pseudorandom code is machined on a scale so as to detect received light intensity associated with the pseudorandom code. The signal processing device calculates an absolute position or an absolute angle for the pseudorandom code using a reference table. The phase of the pseudorandom code is finely divided so as to improve measurement resolution and accuracy.
In general, measurement data for positions or angles obtained by these encoders are transmitted to a host system depending on a data request signal from an external host system. For example, the host system is an industrial apparatus using an encoder and executes positioning control of the object based on measurement data obtained from the encoder. Here, in such an encoder, a measurement error caused by a measurement delay time, i.e., a measurement error caused by the product of a moving speed and a delay time may occur when the object is moving. As a technique for correcting such a measurement error, Japanese Patent Laid-Open No. H8-261794 discloses an encoder that estimates the amount of movement of an object in a delay time required for outputting position data using previously-sampled position data so as to correct currently-sampled position data. Also, Japanese Patent Laid-Open No. 2007-71865 discloses an encoder output interpolation method that measures a time from A/D conversion sampling to data request in response to a data request made from the outside and then interpolates position data before and after the data request so as to output position data.
In recent years, there has been increasing the moving speed or rotational speed of the object although highly-accurate position or angle measurement is required for industrial apparatuses or the like. In association with this, a measurement error caused by the measurement delay time of an encoder has been increasing, resulting in a difficulty in highly-accurate measurement. Here, the encoder disclosed in Japanese Patent Laid-Open No. H8-261794 performs signal processing by starting measurement in response to a data request signal from the host system and then outputs position data by correcting an error due to a delay time. However, when the object is in an acceleration motion, an error between speed information for use in correcting a positional error and the actual speed of the object increases, resulting in a difficulty in outputting an accurate position or angle. On the other hand, the encoder disclosed in Japanese Patent Laid-Open No. 2007-71865 requires position data before and after the data request. However, if a time interval for outputting position data is coarse, interpolation accuracy of position data may deteriorate, resulting in a difficulty in outputting an accurate position or angle. In contrast, if the cycle of a data request signal output from the host system is shortened, the amount of output data from the encoder increases, resulting in an increase in a computation load on the host system. Consequently, the host system is complicated and expensive.